Auditing airtightness: The 101 on blower door tests

Did you know that the average home has enough air leakage to add up to a two-foot-square hole¹? That’s the equivalent to leaving a medium-sized window open 24 hours a day¹. Most homeowners would probably notice if they left a window open all day, but when the window-sized leak is made up of hundreds of smaller gaps throughout your home, it’s harder to pinpoint. For this reason, it is important to identify those leaks so they can be fixed—saving you money, making your home or apartment more comfortable and increasing your energy efficiency. One way to accomplish this is through calculating the airtightness through a blower door test.

What is a Blower Door Test?

A blower door test, also known as an infiltrometer, uses a high-powered fan and a special machine to measure the airtightness of a building and identify potential leaks in the air barrier. Aided by a computer, the fan depressurizes the structure, and the pressure gauge reveals the level of tightness in the space. In other words, the fan is mounted to the frame of an exterior door, typically the main doorway, and it “sucks” the air out of the building, drawing air from outside into any existing leak spots².

How does it work?

Experts recommend using a calibrated door with multiple gauges to measure the amount of air pulled out the house by the fan. According to energy.gov, this is because the calibrated blower door's data allows the auditor to quantify the amount of air leakage and the effectiveness of any air-sealing job¹.

Why is this useful?

Once the house or building is depressurized, energy auditors rely on smoke tools or infrared imaging to help locate any leaks. Once auditors understand where the leaks are, it is up to the homeowner or contractor to determine how to fix the affected area. Repairing the leaky spots and establishing the proper building tightness leads to a more comfortable home in the following ways:

Reducing energy consumption due to air leakage
Avoiding moisture condensation problems
Avoiding uncomfortable drafts caused by cold air leaking in from the outdoors
Determining how much mechanical ventilation might be needed to provide acceptable indoor air quality².

How do air barriers help?

An air barrier is defined as a material or system of materials designed to control airflow between conditioned and unconditioned spaces. It serves as the primary air enclosure boundary separating indoor and outdoor air. In multifamily construction, the air barrier system also separates the conditioned air from any given unit and adjacent units. One potential option for air barrier assemblies involves using building wraps and other weather-resistant components to guard against airflow.

While several materials can impede air movement through a wall assembly, certain technologies perform better than others. Today, building wraps are popular options due to their history of high performance and cost effectiveness. However, proper installation is critical in order for an air barrier system to work as intended. Sealing all laps and penetrations with the proper tape can improve the building wrap’s performance by 20 percent. Horizontal laps are just as important as vertical laps because windblown rain can travel sideways or even up and over an improperly installed lap. Any tears and holes should be sealed with manufacturer-recommended tapes, and all windows and doors should be properly flashed. The goal should be to create a continuous building envelope free from any penetrations through which air could potentially pass.

As an added benefit, some wraps such as TYPAR Building Wrap™, provide moisture control in wall cavities, breathability and up to 6 months of UV protection for revolving construction cycles.

What about multifamily housing?

The use of air barriers in commercial construction is growing, driven by advances in building codes and increased awareness of their ability to support sustainable, comfortable buildings. However, not all air barriers are equal in performance or design, and there is not one solution suitable for all climates, regions, and project conditions.

Understanding how air-barrier materials and systems are evaluated, and knowing their performance characteristics, helps design professionals find the right solution for their project needs. Approaching air barriers from a holistic view and evaluating the entire system—rather than just an individual material—results in a tighter and far more durable enclosure that’s more efficient, saves energy and reduces the cost of monthly utilities—it’s a win-win for occupants and the planet we all share.

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